To break up the awkward silence at the start of a recent Overcoming Bias meetup, I asked everyone present to tell their rationalist origin story - a key event or fact that played a role in their first beginning to aspire to rationality. This worked surprisingly well (and I would recommend it for future meetups).
I think I've already told enough of my own origin story on Overcoming Bias: how I was digging in my parents' yard as a kid and found a tarnished silver amulet inscribed with Bayes's Theorem, and how I wore it to bed that night and dreamed of a woman in white, holding an ancient leather-bound book called Judgment Under Uncertainty: Heuristics and Biases (eds. D. Kahneman, P. Slovic, and A. Tversky, 1982)... but there's no need to go into that again.
So, seriously... how did you originally go down that road?
Added: For some odd reason, many of the commenters here seem to have had a single experience in common - namely, at some point, encountering Overcoming Bias... But I'm especially interested in what it takes to get the transition started - crossing the first divide. This would be very valuable knowledge if it can be generalized. If that did happen at OB, please try to specify what was the crucial "Aha!" insight (down to the specific post if possible).
I never believed in God, even though my parents are casually religious. The idea was simply prohibited by absurdity heuristics. At the same time, I was surrounded by believers in supernatural, alternative medicine, and had a couple of memories of apparently supernatural events. The specific God was absurd, but the invisible dragon of supernatural explanation was clearly true. I knew things normal people didn't, I knew that my alternative medicine worked while all those silly doctors didn't believe in it, I knew that supernatural exists. This gave a clear feeling of superiority.
I started to part with supernatural at University, on Traditional Rationalist grounds. I studied physics, and there was nowhere for supernatural to hide. Mystical retreated in a dark corner of the garage, not allowed to touch real things, not allowed to show in specific tricks, but still lingering as uncertainty. I called myself agnostic back then, taking pride in having an open mind, not excluding the supernatural or even a more abstract God, while not believing in them.
The systematic breakthrough started less than two years ago, when I began thinking about AI. Before then it didn't occur to me that my own beliefs can be treated as reductionistic phenomena, something that has to obey certain laws, which I can reason about, not just with. The supernatural and religion turned out to be mere symptoms of a more important problem, poor mental hygiene, and in their explicit form left the list of matters of concern.